Prior art modulator circuit designs have proposed using bipolar transistor circuits (U.S. Pat. No. 4,359,650) and avalanche transistor circuits (U.S. Pat No. 3,686,516). Such designs have been limited in rise time and fall time of operation resulting in a limited repetition rate. Previous switch designs used switch housekeeping power supplies floating on or near the AC output voltage. The bias supplies require a transformer with a secondary winding, rectifier and filter capacitor for each switch section. The secondaries and circuitry add stray capacitance which is a detriment to high speed switching. The rise times and repetition rates of operation from known modulator circuits has not been fast enough for all applications particularly those where very fast response modulators are used to drive Q-switches and Pockels cells. There is, therefore, a need for an improved modulator circuit which will overcome these limitations.